فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri - Paris Observatory

A concept used for checking the stability of a group of mass
such as a → cluster of galaxies
or a → star cluster.
The crossing time is given by tc = R/V, where
R is the average projected radial distance of group members
from the center of mass and V the Gaussian dispersion in
internal velocity.